Axle assembly with torque distribution drive mechanism

ABSTRACT

An axle assembly with a differential assembly, a housing and a transmission. The transmission has a first and second planetary gearsets that have associated (i.e., first and second) ring gears, planet carriers and sun gears. The first planet carrier is coupled to a differential carrier of the differential assembly for common rotation. The second ring gear is non-rotatably coupled to the housing. The second planet carrier is coupled to the second differential output for common rotation. The second sun gear is coupled to the first sun gear for common rotation.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application is a continuation of U.S. patent application Ser. No.13/835,043 filed Mar. 15, 2013, which is a continuation-in-part of U.S.patent application Ser. No. 13/182,153 filed Jul. 13, 2011 entitled“Axle Assembly With Torque Distribution Drive Mechanism”, which claimsthe benefit of U.S. Provisional Patent Application Ser. No. 61/364,072filed Jul. 14, 2010 entitled “Torque Distribution Drive Mechanism” andU.S. Provisional Patent Application Ser. No. 61/468,809 filed Mar. 29,2011 entitled “Torque Distribution Drive Mechanism”. The disclosure ofeach of the above-identified patent applications is incorporated byreference as if fully set forth in detail herein.

FIELD

The present disclosure relates to an axle assembly and to a vehiclehaving a torque distribution drive mechanism.

BACKGROUND OF THE DISCLOSURE

One means for correcting or reducing understeer or oversteer slide in avehicle is a torque-vectoring differential (TVD). TVD's are typicallyelectronically-controlled differentials that are capable of creating amoment about the center of gravity of a vehicle independent of the speedof the vehicle wheels that would be employed to correct or reduce theundersteer or oversteer slide.

U.S. Pat. No. 7,491,147 discloses an engine-driven TVD that employs apair of speed control mechanisms that are disposed on opposite sides ofa differential mechanism. Each speed control mechanism comprises a(spur) gear reduction and a friction clutch. The gear reductiontransmits rotary power from a differential case of the differentialmechanism to the friction clutch, and from the friction clutch to anassociated (axle) output shaft.

Similarly, U.S. Pat. No. 7,238,140 discloses an engine-driven TVD thatemploys a pair of torque diverters that are disposed on opposite sidesof a differential mechanism. Each torque diverter comprises a gearreduction and a magnetic particle brake. The gear reduction transmitsrotary power from a differential case of the differential mechanism toan output member that is coupled to an associated axle output shaft forrotation therewith. The magnetic particle brake is configured toselectively brake the output member of the gear reduction.

U.S. Patent Application Publication No. 2010/0323837 discloses anelectrically-driven TVD having a pair of planetary transmissions, anelectric motor, and a sleeve that controls the operation of theplanetary transmissions. The TVD can be operated in a first mode inwhich the TVD is configured as an open differential that is driven bythe electric motor, and a second mode in which the TVD produces a torquevectoring output.

While such configurations can be effective for performing a torquevectoring function in which rotary power can be re-allocated across thedifferential mechanism from one axle shaft to the other, TVD's arenonetheless susceptible to improvement.

SUMMARY OF THE DISCLOSURE

This section provides a general summary of the disclosure, and is not acomprehensive disclosure of its full scope or all of its features.

In one form, the present teachings provide an axle assembly with aninput member, a first planetary gear set, a differential assembly, and asecond planetary gear set. The first planetary gear set has a firsttransmission input that is driven by the input member. The differentialassembly has a differential carrier and first and second differentialoutput members received in the differential carrier. The secondplanetary gear set has a planet carrier coupled to the differentialcarrier for common rotation. A sun gear of the first planetary gear setis non-rotatably coupled to a sun gear of the second planetary gear set.

In another form, the present teachings provide an axle assembly with aninput member, a first planetary gear set, a differential assembly and asecond planetary gear set. The first planetary gear set has a firsttransmission input, a first sun gear, a first ring gear, a plurality offirst planet gears, and a first planet carrier. The first transmissioninput is driven by the input member. The first planet gears aremeshingly engaged to the first sun gear and the first ring gear. Thefirst planet carrier supports the first planet gears for rotation. Thedifferential assembly has a differential carrier and first and secondoutput members that are received in the differential carrier. The secondplanetary gear set has a second planet carrier coupled to thedifferential carrier for common rotation. The input member, the firstplanetary gear set and the second planetary gear set are disposed on acommon axial end of the differential carrier. The axle assembly isoperable in a mode in which the first and second planet carriers arerotatably decoupled from one another.

The first planetary gear set has a first transmission input that isdriven by the input member. The differential assembly has a differentialcarrier and first and second output members received in the differentialcarrier. The second planetary gear set has a planet carrier coupled tothe differential carrier for common rotation. The input member, thefirst planetary gear set and the second planetary gear set are disposedon a common axial end of the differential carrier.

In another form, the present teachings provide an axle assembly thatincludes a motor, an input member driven by the motor, a differentialassembly, a transmission and a shiftable element. The differentialassembly has a differential carrier and first and second differentialoutputs received in the differential case. The transmission receivesrotary power from the input member. The shiftable element is axiallymovable between a first position and a second position. Positioning ofthe shiftable element in the first position couples the transmission tothe differential assembly to establish a torque vectoring mode in whichthe transmission applies an equal but oppositely directed torque to thefirst and second differential outputs. Positioning of the shiftableelement in the second position couples the transmission to thedifferential assembly to directly drive the differential carrier.

In still another form, the present teachings provide an actuator forlinear displacement of a part in a mechanism that is switchable betweenat least two modes. The actuator includes an input member arranged to beoperably coupled to a drive member, an output member arranged to beoperably coupled to the switch, and a converting member for converting arotational movement of the drive member into a linear movement of theswitch. The converting member includes a cylindrical cam having a camgroove extending along at least a part of a periphery of the cam, and acam follower arranged to move in the cam groove. The cam is operablycoupled to the input member, and the cam follower is operably coupled tothe output member. The groove includes a first groove portion extendingparallel to a transverse plane that is perpendicular to a longitudinalaxis of the cam, a second groove portion extending parallel to thetransverse plane, and a third groove portion extending between the firstand second groove portion, and extending in a direction along theperiphery of the cam forming an angle of more than 0° in relation to thetransverse plane.

In a further form, the present disclosure provides an axle assembly witha motor, a differential assembly, a housing, a transmission and areduction gearset. The motor has an output shaft disposed along anoutput shaft axis. The differential assembly has a differential carrierand first and second differential outputs that are received in thedifferential carrier which are rotatable about an output axis. Thetransmission is received in the housing and has first and secondplanetary gearsets. The first planetary gearset has a first ring gear, afirst planet carrier and a first sun gear. The first planet carrier iscoupled to the differential carrier for common rotation. The secondplanetary gearset has a second ring gear, a second planet carrier and asecond sun gear. The second ring gear is non-rotatably coupled to thehousing. The second planet carrier is coupled to the second differentialoutput for common rotation. The second sun gear is coupled to the firstsun gear for common rotation. The reduction gearset is disposed betweenthe output shaft and the first ring gear and includes a first gear,which is coupled to the output shaft for rotation therewith, and asecond gear that is coupled to the first ring gear for rotationtherewith.

In yet another form, the present teachings provide an axle assemblyhaving first and second axle shafts, a differential assembly, a housingand a transmission. The differential assembly has a differential carrierand first and second differential outputs received in the differentialcarrier that are rotatable about an output axis. The first differentialoutput is drivingly coupled to the first axle shaft. The seconddifferential output is drivingly coupled to the second axle shaft. Thetransmission is received in the housing and has first and secondplanetary gearsets. The first planetary gearset has a first ring gear, afirst planet carrier and a first sun gear. The first planet carrier iscoupled to the differential carrier for common rotation. The secondplanetary gearset has a second ring gear, a second planet carrier and asecond sun gear. The second ring gear is non-rotatably coupled to thehousing. The second planet carrier is coupled to the second differentialoutput and the second axle shaft for common rotation. The second sungear is coupled to the first sun gear for common rotation.

Further areas of applicability will become apparent from the descriptionprovided herein. The description and specific examples in this summaryare intended for purposes of illustration only and are not intended tolimit the scope of the present disclosure.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawings described herein are for illustrative purposes only ofselected embodiments and not all possible implementations, and are notintended to limit the scope of the present disclosure.

FIG. 1 diagrammatically illustrates a cross-sectional view of a torquedistribution drive mechanism according to a first embodiment;

FIG. 2 diagrammatically illustrates a cross-sectional view of a torquedistribution drive mechanism operable in several modes according to asecond embodiment;

FIG. 3 diagrammatically illustrates a cross-sectional view of a torquedistribution drive mechanism operable in several modes according to athird embodiment.

FIG. 4 is a disassembled view of an actuator according to an embodimentof the disclosure;

FIG. 5 is a partially disassembled view of the actuator of FIG. 4;

FIG. 6 is a perspective view of the actuator of FIG. 6;

FIG. 7 diagrammatically illustrates a cross-sectional view of a torquedistribution drive mechanism according to a fourth embodiment;

FIG. 8 is a perspective view of a portion of the torque distributiondrive mechanism of FIG. 7;

FIG. 9 is a rear elevation view of a portion of the torque distributiondrive mechanism of FIG. 7;

FIG. 10 is a perspective view of a portion of the torque distributiondrive mechanism of FIG. 7;

FIG. 11 is a longitudinal section view of a portion of another axleassembly constructed in accordance with the teachings of the presentdisclosure; and

FIG. 12 is an enlarged portion of FIG. 11.

Corresponding reference numerals indicate corresponding parts throughoutthe several views of the drawings.

DETAILED DESCRIPTION

With reference to FIG. 1, an axle assembly constructed in accordancewith the teachings of the present disclosure is generally indicated byreference numeral 10. The axle assembly 10, which could be a front axleassembly or a rear axle assembly of a vehicle 12 for example. The axleassembly 10 can include a torque distribution drive mechanism 14 a thatmay be used for transmitting torque to a first output member 16 and asecond output member 18, which are illustrated as being first and secondaxle shafts, respectively, in the present example. For example, thefirst output member 16 may be coupled to a left wheel 20 and the secondoutput member 18 may be coupled to a right wheel 22 of the axle assembly10. In particular and as further explained below, the torquedistribution drive mechanism 14 a may be used for torque vectoring, thatis, to generate a torque difference between the first and second outputmembers 16 and 18.

The torque distribution drive mechanism 14 a can comprise a dualplanetary gear set 30 and a drive member 32.

The dual planetary gear set 30 can be co-axially mounted with respect tothe first and second output members 16 and 18 and/or a differentialassembly 36. The dual planetary gear set 30 can comprise a firstplanetary gear set 40 and a second planetary gear set 42. The first andsecond planetary gear sets 40 and 42 can have identical gear ratios andcan be configured such that one or more of the components of the firstplanetary gear set 40 is/are interchangeable with associatedcomponent(s) of the second planetary gear set 42.

The first planetary gear set 40 can comprise a first sun gear 50, aplurality of first planet gears 52, a first ring gear 54, and a firstplanet carrier 56. The first sun gear 50 can be a generally hollowstructure that can be mounted concentrically about the first outputmember 16. The first planet gears 52 can be spaced circumferentiallyabout the first sun gear 50 such that teeth of the first planet gears 52meshingly engage teeth of the first sun gear 50. Likewise, the firstring gear 54 can be disposed concentrically about the first planet gears52 such that the teeth of the first planet gears 52 meshingly engageteeth on the first ring gear 54. The first ring gear 54 can be rotatablydisposed in a transmission housing 58 that can be non-rotatably coupledto a differential housing 60 that houses the differential assembly 36.The first planet carrier 56 can include a first carrier body 62 and aplurality of first pins 64 that can be fixedly coupled to the firstcarrier body 62. The first carrier body 62 can be coupled to the firstoutput member 16 such that the first carrier body 62 and the firstoutput member 16 co-rotate. Any suitable means may be employed to couplethe first carrier body 62 to the first output member 16, including weldsand mating teeth or splines. Each of the first pins 64 can be receivedinto an associated one of the first planet gears 52 and can support theassociated one of the first planet gears 52 for rotation about alongitudinal axis of the first pin 64.

The second planetary gear set 42 can comprise a second sun gear 70, aplurality of second planet gears 72, a second ring gear 74, and a secondplanet carrier 76. The second sun gear 70 can be a generally hollowstructure that can be mounted concentrically about the first outputmember 16. The second sun gear 70 can be non-rotatably coupled to thefirst sun gear 50 (e.g., the first and second sun gears 50 and 70 can beintegrally and unitarily formed). The second planet gears 72 can bespaced circumferentially about the second sun gear 70 such that theteeth on the second planet gears meshingly engage teeth of the secondsun gear 70. The second ring gear 74 can be disposed concentricallyabout the second planet gears 72 such that the teeth of the secondplanet gears 72 meshingly engage teeth on the second ring gear 74. Thesecond ring gear 74 can be non-rotatably coupled to the transmissionhousing 58. The second planet carrier 76 can include a second carrierbody 82 and a plurality of second pins 84 that can be fixedly coupled tothe second carrier body 82. The second carrier body 82 can be coupled toa housing or differential carrier 83 of the differential assembly 36such that the second carrier body 82 and the differential carrier 83co-rotate. Each of the second pins 84 can be received into an associatedone of the second planet gears 72 and can support the associated one ofthe second planet gears 72 for rotation about a longitudinal axis of thesecond pin 84.

The first and second planetary gear sets 40 and 42 can be co-alignedabout a common longitudinal axis (i.e., an axis that can extend throughthe first and second sun gears 50 and 70) and can be offset from oneanother axially along the common longitudinal axis 85.

The drive member 32 can be any means for providing a rotary input to thedual planetary gear set 30, such as an electric or hydraulic motor, andcan be employed to drive an input member 86 that transmits rotary powerto a transmission input of the first planetary gear set 40. In theexample provided, the transmission input is integral with the first ringgear 54, and the input member 86 is coupled to the first ring gear 54for common rotation and includes a plurality of teeth that meshinglyengage teeth of a reduction gear 88 that is mounted on an output shaft90 of the drive member 32. The input member 86 can be a discretecomponent that can be non-rotatably coupled to the first ring gear 54,but in the example provided, the input member 86 and the first ring gear54 are unitarily formed as a single discrete component.

In addition to the differential housing 60 and the differential carrier83, the differential assembly 36 can include a means for transmittingrotary power from the differential carrier 83 to the first and secondoutput members 16 and 18. The rotary power transmitting means caninclude a first differential output 100 and a second differential output102. In the particular example provided, the rotary power transmittingmeans comprises a differential gear set 104 that is housed in thedifferential carrier 83 and which has a first side gear 106, a secondside gear 108, a cross-pin 110 and a plurality of pinion gears 112. Thefirst and second side gears 106 and 108 can be rotatably disposed abouta rotational axis of the differential carrier 83 and can comprise thefirst and second differential outputs 100 and 102, respectively. Thefirst output member 16 can be coupled to the first side gear 106 forcommon rotation, while the second output member 18 can be coupled to thesecond side gear 108 for common rotation. The cross-pin 110 can bemounted to the differential carrier 83 generally perpendicular to therotational axis of the differential carrier 83. The pinion gears 112 canbe rotatably mounted on the cross-pin 110 and meshingly engaged with thefirst and second side gears 106 and 108.

While the differential assembly 36 has been illustrated as employingbevel pinions and side gears, it will be appreciated that other types ofdifferential mechanisms could be employed, including differentialmechanisms that employ helical pinion and side gears or planetary gearsets.

Optionally, the differential assembly 36 may be coupled to a main orprimary drive of the vehicle 12. In the particular example provided, theprimary drive of the vehicle comprises an engine 120 that is employed todrive the differential assembly 36. In this regard, rotary powerproduced by the engine 120 can be transmitted in a conventional mannerto the differential carrier 83 to drive the first and second outputmembers 16 and 18 (i.e., via the differential carrier 83 and thedifferential gear set 104). In this way, the drive member 32 may serveas a complement to the primary drive of the vehicle 12 such that when anauxiliary torque is simultaneously generated by the drive member 32, theauxiliary torque will be superimposed to the first and second outputtorques induced by the primary drive as further explained in thefollowing.

When the drive member 32 is activated (i.e., when the output shaft 90 ofthe drive member 32 rotates in the example provided), the drive member32, the reduction gear 88 and the input member 86 can cooperate to applyrotary power to the first ring gear 54 of the first planetary gear set40. The rotary power received by the first ring gear 54 is transmittedvia the first planet gears 52 and the first planet carrier 56 to thefirst output member 16, while an opposite reaction is applied to thefirst sun gear 50 such that the first sun gear 50 rotates in a directionthat is opposite to the first planet carrier 56. Rotation of the firstsun gear 50 causes corresponding rotation of the second sun gear 70 tothereby drive the second planet gears 72. Because the second ring gear74 is rotationally fixed to the transmission housing 58, rotation of thesecond planet gears 72 causes rotation of the second planet carrier 76in a direction that is opposite to the direction of rotation of thefirst planet carrier 56. Accordingly, the magnitude of the rotary power(i.e., torque) that is transmitted from the second planet carrier 76 tothe differential carrier 83 (and through the differential assembly 36 tothe second output member 18) is equal but opposite to the magnitude ofthe rotary power (i.e., torque) that is transmitted from the firstplanet carrier 56 to the first output member 16.

Thus, as a result, the torque induced by the drive member 32 to thefirst and second output members 16 and 18, respectively, iscounter-directed. Moreover, since the first and second planetary gearsets 40 and 42 are operably coupled via the differential assembly 36,the magnitude of the induced torque at the first and second outputmembers 16 and 18 is substantially equal. For example, if a positivelydirected torque is transmitted to the first output member 16 (viarotation of the output shaft 90 of the drive member 32 in a firstrotational direction), an equal negative torque is transmitted to thesecond output member 18. Similarly, if a negatively directed torque istransmitted to the first output member 16 (via rotation of the outputshaft 90 of the drive member 32 in a second rotational directionopposite the first rotational direction), an equal positive torque istransmitted to the second output member 18. In other words, the torquedistribution drive mechanism 14 a may be employed to generate a torquedifference between the first and second differential outputs 100 and102, which is communicated to the left and the right wheels 20 and 22,respectively, through the first and second output members 16 and 18,respectively.

In situations where the drive member 32 is activated when rotary poweris transmitted from the primary drive (i.e., engine 120 in the exampleillustrated) to the differential assembly 36, the torque transmitted bythe torque distribution drive mechanism 14 a will act as an offsettorque which is superposed to the input torque transmitted to the axleassembly 10 from the primary drive. Stated another way, the input torquefrom the primary drive is distributed via the differential assembly 36such that a first drive torque is applied via the first differentialoutput 100 to the first output member 16 and a second drive torque isapplied via the second differential output 102 to the second outputmember 18, while a supplemental torque induced by the drive member 32 isdistributed via the dual planetary gear set 30 such that a firstvectoring torque is applied to the first output member 16 and a secondvectoring torque (which is equal and opposite to the first vectoringtorque in the example provided) is applied to the second output member18 (via the differential assembly 36). The net torque acting on thefirst output member 16 is the sum of the first drive torque and thefirst vectoring torque, while the net torque acting on the second outputmember 18 is the sum of the second drive torque and the second vectoringtorque.

As an example, the torque distribution drive mechanism 14 a may subtracta torque from the left wheel 20 and add a corresponding torque to theright wheel 22 when the motorized vehicle 12 turns left, and maysubtract a torque from the right wheel 22 and add a corresponding torqueto the left wheel 20 when the motorized vehicle 12 turns right toimprove the turning behavior of the vehicle 12 and decrease its turningradius.

Those of skill in the art will appreciate that the configuration of thedual planetary gear set 30 causes the first and second sun gears 50 and70 to experience the highest rotational velocity, while the first ringgear 54 rotates at a somewhat slower rotational velocity, and the firstand second planet carriers 56 and 76 rotate at a rotational velocitythat is slower than that of the first ring gear 54. In this way afavorable gear ratio, such as a gear ratio of about 1:1.5 to about1:2.0, can be achieved between the first ring gear 54 and the firstoutput member 16. As a result, the size of the gears of the dualplanetary gear set 30 may be made small. For example, the diameter ofthe first and second planet gears 52 and 72 may be as small as about 30mm. In this way, the size of the dual planetary gear set 30 may besmall, and thereby the torque distribution drive mechanism 14 a may bemade compact and lightweight.

The drive member 32 is intended to be activated (e.g., automatically oron an as-needed basis) when the vehicle 12 turns. During straightforward driving, the drive member 32 is therefore non-activated topermit the vehicle 12 to be propelled in a forward direction by theengine 120. In such a situation, the differential assembly 36, whichreceives the input torque from the engine 120, transmits a substantiallyequal torque to the first output member 16 and the second output member18. In turn, a substantially equal torque is transmitted to the firstand second planetary carriers 56 and 76 which rotate with asubstantially equal speed. As an effect, and due to the identicalplanetary gear sets 40 and 42, there will be no relative motion betweenthe first and second ring gears 54 and 74, meaning that almost no effector torque is transferred to the first and second ring gears 54 and 74.In other words, neither the first ring gear 54 nor the second ring gear74 will rotate. In this way, the output shaft 90 of the drive member 32will not move and losses during straight forward driving are in this wayminimized.

While the input member 86 has been illustrated and described as directlyengaging the reduction gear 88, it will be appreciated that one or morereduction stages could be disposed between the input member 86 and thereduction gear 88 or that the input member 86 could be directly drivenby the drive member 32.

With reference to FIG. 2, another axle assembly constructed inaccordance with the teachings of the present disclosure is generallyindicated by reference numeral 10 b. The axle assembly 10 b can begenerally similar to the axle assembly 10 of FIG. 1 except as notedherein. In this example, the axle assembly 10 b comprises a torquedistribution drive mechanism 14 b that is selectively operable in aplurality of operational modes including a torque vectoring mode, adrive mode and a neutral mode. The torque distribution drive mechanism14 b can be structurally similar to the torque distribution drivemechanism 14 a of FIG. 1, except that the input member 86 b is rotatablerelative to the first ring gear 54 b and an actuator 150 is employed tocontrol the operational state of the torque distribution drive mechanism14 b. The input member 86 b can comprise a crown gear that can berotatably mounted about the first output member 16 and the firstplanetary gear set 40 b. The actuator 150 can include a shift sleeve 152that can form the transmission input. The shift sleeve 152 can have atoothed exterior surface 154, which can be non-rotatably but axiallyslidably engaged to a matingly toothed interior surface 156 of the inputmember 86 b, a set of first internal teeth 160, which can be matinglyengaged to corresponding teeth 162 formed on the first ring gear 54 b,and a set of second internal teeth 164 that can be matingly engaged tocorresponding teeth 166 formed on the second planet carrier 76 b.

In the torque vectoring mode, the shift sleeve 152 can be positioned ina first position to couple the input member 86 b to the first ring gear54 b (via engagement of the set of first internal teeth 160 to the teeth162 on the first ring gear 54 b) such that the input member 86 b, theshift sleeve 152 and the first ring gear 54 b co-rotate. It will beappreciated that the set of second internal teeth 164 are disengagedfrom the teeth 166 on the second planet carrier 76 b when the shiftsleeve 152 is in the first position. Accordingly, it will be appreciatedthat operation of the torque distribution drive mechanism 14 b in thetorque vectoring mode is substantially similar to the operation of thetorque distribution drive mechanism 14 a (FIG. 1). In this regard, thedrive member 32 may be selectively activated to induce a torquedifference between the first and second output members 16 and 18 aspreviously explained.

In the drive mode, the shift sleeve 152 can be positioned in a secondposition to couple the input member 86 b to the second planet carrier 76b (via engagement of the set of second internal teeth 164 with the teeth166 on the second planet carrier 76 b) such that rotary power providedby the drive member 32 is input to differential carrier 83 and appliedto the first and second output members 16 and 18 via the differentialassembly 36. It will be appreciated that the set of first internal teeth160 on the shift sleeve 152 can be disengaged from the teeth 162 on thefirst ring gear 54 b when the shift sleeve 152 is in the secondposition. It will also be appreciated that rotary power provided by thedrive member 32 when the torque distribution drive mechanism 14 b isoperated in the drive mode is employed for propulsive power to propel(or aid in propelling) the vehicle 12.

In the neutral mode, the shift sleeve 152 can uncouple the input member86 b from the first ring gear 54 b and the second planet carrier 76 bsuch that the input member 86 b is decoupled from the first planetarygear set 40 b, the second planetary gear set 42 b, and the differentialcarrier 83. In the example provided, the shift sleeve 152 can bepositioned in a third position between the first and second positionssuch that the sets of first and second internal teeth 160 and 164 aredisposed axially between and disengaged from the teeth 162 on the firstring gear 54 b and the teeth 166 on the second planet carrier 76 b.Accordingly, placement of the shift sleeve 152 in the third positiondecouples the drive member 32 from the first planetary gear set 40 b,the second planetary gear set 42 b and the differential carrier 83.

With reference to FIG. 3, yet another axle assembly constructed inaccordance with the teachings of the present disclosure is generallyindicated by reference numeral 10 c. The axle assembly 10 c can begenerally similar to the axle assembly 10 b of FIG. 2 except as notedherein. In this example, the axle assembly 10 c comprises a torquedistribution drive mechanism 14 c that is selectively operable in aplurality of operational modes including a torque vectoring mode, adrive mode, a neutral mode and a low speed drive mode. The torquedistribution drive mechanism 14 c can be structurally similar to thetorque distribution drive mechanism 14 b of FIG. 2, except that theshift sleeve 152 c can have a third set of internal teeth 170 that canbe selectively engaged to teeth 172 of a toothed element 174 that iscoupled to the first and second sun gears 50 and 70 for rotationtherewith. The set of third internal teeth 170 are not engaged to anyother structure when the torque distribution drive mechanism 14 c isoperated in the torque vectoring, drive, and neutral modes and as such,the operation of the torque distribution drive mechanism 14 c issubstantially similar to the operation of torque distribution drivemechanism of FIG. 2 in these modes.

In the low speed drive mode, however, the shift sleeve 152 c can bepositioned in a fourth position to couple the input member 86 b to thefirst and second sun gears 50 and 70 (via the engagement of the set ofthird internal teeth 170 to the teeth 172 on the element 174) such thatthe input member 86 b, the shift sleeve 152 c, the element 174, and thefirst and second sun gears 50 and 70 co-rotate. In this mode, the secondplanetary gear set 42 b is employed as a gear reduction which causes thesecond planet carrier 76 b to rotate at a rotational speed that is lowerthan the rotational speed of the second sun gear 70. It will beappreciated that the sets of first and second internal teeth 160 and 164are disengaged from the teeth 162 on the first ring gear 54 b and theteeth 166 on the second planet carrier 76 b when the shift sleeve 152 cis in the fourth position.

Those of skill in the art will appreciate that rotary power is input tothe dual planetary gear set 30 b at different locations when torquedistribution drive mechanism 14 c is operated in the drive mode and inthe low speed drive. In this regard, rotary power is input to the secondplanet carrier 76 b in the drive mode, and input to the first and secondsun gears 50 and 70 in the low speed drive. Accordingly, it will beappreciated that the differential carrier 83 will rotate at a slowerrotational velocity (for a given rotational speed of the output shaft 90of the drive member 32) in the low speed drive as compared to the drivemode. In this regard, rotation of the first and second sun gears 50 and70 when the torque distribution drive mechanism 14 c is operated in thelow speed drive will cause corresponding rotation of the second planetgears 72, which in turn drives the rotation of the second planet carrier76 and the differential carrier 83. Stated another way, a gear reductionis disposed between the rotary input (i.e., the element 174) and thedifferential carrier 83 when the torque distribution drive mechanism 14c is operated in the low speed drive, and no gear reduction is disposedbetween the rotary input (i.e., the second planet carrier 76 b) and thedifferential carrier 83 when the torque distribution drive mechanism 14c is operated in the drive mode.

The dimension of the shift sleeve 152 in the axial direction and thewidth and spacing of the several sets of teeth can be selected such thatat most one of the sets of internal teeth 160, 164 and 170 is permittedto engage the corresponding teeth 162, 166 and 172, respectively, at thesame time. Additionally or alternatively, the pitch diameters of themating sets of teeth can be sized differentially to permit certain teethto slide over other teeth where engagement of those teeth are notdesired. For example, the pitch diameter of the set of second internalteeth 164 is larger than the pitch diameter of the set of third internalteeth 170 so that the set of second internal teeth 164 may pass axiallyacross the teeth 172 on the element 174 that is rotatably coupled to thefirst and second sun gears 50 and 70.

It is also possible to construct a torque distribution drive mechanismwhich is operable in the drive and neutral modes only. In such a case,the dual planetary gear set 30 may be omitted since its functionalitiesof generating counter-directed torques in the torque vectoring mode andreduced speed input to the differential carrier 83 in the low speeddrive are not needed.

In such a situation, the torque distribution drive mechanism maycomprise a drive member, a crown gear operably coupled to the drivemember, a switching member rotationally coupled to the crown gear forswitching between the drive mode and the neutral gear mode, and adifferential being operably coupled to a first and a second outputmember. The shift sleeve 152 or other switching member may be arrangedto engage with the differential. In particular, the switching member maybe arranged to engage with a differential carrier of the differential.Further, the switching member may be arranged to be in a position whereit is uncoupled from the differential.

Similar to the embodiments of FIGS. 2 and 3, disclosed above, theswitching element may comprise a shift sleeve rotationally coupled tothe crown gear. Further, the switching element may comprise a radiallyextending teeth structure which is arranged on the shift sleeve in aninwards radial direction and which is arranged to engage with a matingteeth structure on the outer surface of the differential carrier. Theshift sleeve may slide along the crown gear in an axial direction. Bysliding the shift sleeve towards the differential, the teeth structureof the shift sleeve may engage with the mating teeth structure on thedifferential carrier. In this way, the torque distribution drivemechanism is operable in the high gear mode. When sliding the shiftsleeve away from the differential, the teeth structure of the switchingmember disengages from the teeth structure on the outer surface of thedifferential carrier. In this way, the drive member will be in a neutralgear since it does not induce any torque to the differential.

An advantage with this construction is that it may be formed in amodular way. That is, the construction may be formed as a module whicheasily may be added to a differential in an existing transmission.

The switching element or shift sleeve in each of the last three examplescan be moved axially by any desired actuator, including conventionalshift fork actuators of the type that are commonly used in transfercases. It will be appreciated, too, that one or more synchronizers canbe incorporated with the shift sleeve to permit the shift sleeve to bedriven (e.g., via the first ring gear or the second planetary carrier)prior to actuation of the drive member 32 such that the rotational speedof the shift sleeve matches the rotational speed of the component towhich the shift sleeve is to be rotationally coupled.

With reference to FIG. 4, an exemplary actuator 200 for translating ashift sleeve is illustrated. The actuator 200 has an input member in theform of a rotational connection 202 to a drive member, such as anelectric DC motor 210, FIG. 6, or other suitable rotational inputdevice. The rotational connection 202 generally comprises a rotationalshaft 300, which is connected to the motor 210. Further, the actuator200 has an output member 400 in the form of a piston or rod. Attached tothe rod 400 is a projection or nub 500. Along a guide portion 600 of therod 400, a cross-section of the rod 400 is non-cylindrical.

A cylindrical cam 700 is arranged on the rotational shaft 300. Aroundthe cylindrical cam 700 a cam groove 800 is formed. The cam groove 800is divided into three groove portions 800 a, 800 b, and 800 c. A firstgroove portion 800 a extends along and about the periphery of the cam700 in a direction parallel to a transverse plane 710 that isperpendicular to a longitudinal axis C of the cam 700. A second grooveportion 800 b also extends along and about the periphery of the cam 700in the direction parallel to the transverse plane 710. A third grooveportion 800 c extends along and about the periphery of the cam 700between the first groove portion 800 a and the second groove portion 800b, and extends in a direction forming an angle of more than 0° inrelation to the transverse plane. Thus, the first and second grooveportions 800 a and 800 b are not inclined, i.e. they each have zeroslope in the axial direction of the cam 700 and relative to thetransverse plane 702, whereas the third groove portion 800 c slopes andextends axially along longitudinal axis C of the cam 700.

A first flange 900 and a second flange 901 are arranged one on each sideof the cylindrical cam 700. A first through-hole 911 in the first flange900 and a second through-hole 921 in the second flange 901 form a guidefor the rod 400. The second through-hole 921 forms a passage with anon-circular cross-section matching the cross section of the guideportion 600 of the rod 400. A third through-hole 931 of the first flange900 and a fourth through-hole 941 of the second flange 901 are arrangedto each receive a respective end of the rotational shaft 300, supportedfor rotation by respective journal bearings 951 and 961. Four distancingor spacer elements 971 are arranged to be placed between the flanges 900and 901.

FIG. 5 illustrates how the parts of the actuator 200 are assembled. Inparticular, it may be seen that the nub 500 is fitted inside the camgroove 800. As the cylindrical cam 700 is rotated by the motor 210, thenub 500 is forced to follow the groove 800. When the nub 500 movesaxially from the first groove 800 a through the third groove portion 800c and to the second groove portion 800 b, the rod is displaced in alinear direction L. Thus, a movement of the cylindrical cam 700 in arotational direction R is converted into a linear displacement in thelinear direction L.

When the nub 500 is positioned in the first groove portion 800 a, whichhas zero slope, an angle between the groove and the rod is 90°. As such,the nub 500 will have no axial or linear forced applied thereto and therod 400 will be kept still in this position. The first groove portion800 a corresponds to a first position of a switch 810 operably coupledto the rod 400. In this first position, the switch 810 ensures that theshift sleeve 152 (FIG. 2) can be positioned in the third position topermit the torque distribution drive mechanism 14 b (FIG. 2) to operatein the drive mode.

If the motor 210 is started, the cylindrical cam 700 rotates in therotational direction R and the nub 500 is moved from the first grooveportion 800 a, along the sloping third groove portion 800 c, to thesecond groove portion 800 b, thereby moving the rod 400 in the lineardirection L. Since the second groove portion 800 b has zero slope, thenub 500 will have no axial or linear force applied thereto and the rod400 will be kept still in this position once the motor 210 is stopped.Thereby, the rod 400 will stop moving and the switch 810 will be held ina second position. In this second position, the switch ensures that theshift sleeve 152 (FIG. 2) can be positioned in the first position topermit the torque distribution drive mechanism 14 b (FIG. 2) to operatein the torque vectoring mode.

The person of ordinary skill in the art will appreciate that a number ofmodifications of the embodiments described herein are possible withoutdeparting from the scope of the disclosure, which is defined in theappended claims

For instance, the actuator 200 has above been described in the contextof a torque distribution mechanism of a motorized vehicle 12, but suchan actuator is equally useful in other constructions. The actuatorcould, e.g., be used in a lock mechanism, wherein the different modescould correspond to a locked state and an unlocked state. Generally, anactuator of the type described above may be used in any context in whicha part is to be linearly displaced quickly and with precision, and inwhich the displacement is to be driven by a drive member giving arotational output.

In the exemplary embodiment described above, the groove 800 has twogroove portions 800 a and 800 c with no inclination. Naturally, morethan two non-inclined groove portions may be formed on the cam 700, eachnon-inclined groove portion corresponding to a position of the part thatis connected to the rod, e.g., a switch. Thus, in a torque distributingdrive mechanism, a groove with three non-inclined groove portions, andtwo inclined groove portions connecting the non-inclined grooveportions, could correspond to three different gear modes, such as apropulsion mode, a torque vectoring mode, and a neutral gear mode.

With reference to FIGS. 7 through 10 of the drawings, another axleassembly 10 d constructed in accordance with the teachings of thepresent disclosure is illustrated. The axle assembly 10 d can include atorque distribution drive mechanism 14 d that can similar to the torquedistribution drive mechanism 14 a of FIG. 1 except as noted. As such,reference numerals employed in FIG. 1 will be employed to indicatecorresponding elements in FIGS. 7 through 10.

In lieu of the drive member 32 and the reduction gear 88 that areemployed in FIG. 1 (the drive member 32 and reduction gear 88 beingarranged about a rotational axis that is parallel to the rotational axesof the differential carrier 83 and the first planet carrier 56), theexample of FIGS. 7 through 10 employs a drive member 32 d and areduction gear 88 d that are arranged about a rotational axis 1300 thatis perpendicular to the rotational axes 85 of the differential carrier83 and the first planet carrier 56. For example, the rotational axis1300 can be orthogonal to a rotational axis 1304 of an engine 120 (orother means for providing rotary power, such as an electric or hydraulicmotor) and the rotational axes 85 of the differential carrier 83 and thefirst planet carrier 56. The engine 120 can drive an input pinion 1306(e.g., via a propshaft (not shown)) that is meshed with a ring gear 1308that can be coupled to the differential carrier 83 in a conventionalmanner.

Configuration of the torque distribution drive mechanism 14 d in thismanner may be advantageous in some situations when space for packagingthe torque distribution drive mechanism into a vehicle is limited.

The drive member 32 d can be any type of motor, such as an AC electricmotor or a DC electric motor, and can have an output shaft 37 d-1 towhich the reduction gear 88 d can be rotatably coupled.

The reduction gear 88 d can be a worm 1312 that can be meshingly engagedto a worm gear 1314. The worm gear 1314 can be rotatably coupled to thefirst ring gear 54 d (e.g., formed on an outer surface of the first ringgear 54 d). The worm 1312 and worm gear 1314 can be relatively small insize but nonetheless provide a relatively large gear reduction ratio.Consequently, the drive member 32 d can be configured to produce arelatively high-speed, low torque output and as such, can be relativelysmaller in diameter than the drive member 32 of FIG. 1.

If desired, the worm 1312 and worm gear 1314 can be configured to beself-locking when the drive member 32 d is not actively powered toeffectively lock the differential assembly 36 d to inhibit speeddifferentiation between the first and second output members 16 and 18.In this regard, locking of the worm 1312 and worm gear 1314 inhibitsrotation of the first ring gear 54 d. Since the second planet carrier 76d and the differential carrier 83 are coupled for rotation, rotation ofthe differential carrier 83 (via rotation of the differential ring gear1308 resulting from rotation of the input pinion 1306) can provide arotary input to the second planet carrier 76 d, which causes the secondplanet gears 72 of the second planetary gear set 42 to rotate within thesecond ring gear 74 and rotate the second sun gear 70. Rotation of thesecond sun gear 70 causes rotation of the first sun gear 50, causingrotation of the first planet gears 52 of the first planetary gear set40, which, in turn, causes the first planet carrier 56 to rotate. Sincethe first planet carrier 56 is coupled to the first output member 16,and since the first and second planetary gear sets 40 and 42 haveidentical gear reduction ratios, the first and second planet carriers 56and 76 rotate at the same rate (i.e., at the rate at which thedifferential carrier 83 rotates). As such, the first output member 16cannot rotate relative to the differential carrier 83 so that thedifferential gear set 104 is locked to the differential carrier 83.

For the worm 1312 and worm gear 1314 to be self-locking, the worm gear1314 cannot “back drive” the worm 1312. As those of skill in the artwill appreciate, the ability for the worm 1312 and worm gear 1314 tolock depends on several factors, including the lead angle, the pressureangle and the coefficient of friction, but often times the analysis canbe reduced to a rough approximation involving the coefficient offriction and the tangent of the lead angle (i.e., self locking iftangent of the lead angle<coefficient of friction).

With specific reference to FIGS. 7 and 10, the dual planetary gear set30 and the reduction gear 88 d can be housed in a housing 1340 that cancomprise a first housing shell 1342 and a second housing shell 1344 thatare fixedly coupled to one another via a set of fasteners (not shown).The drive member 32 d can be mounted to a flange 1348 formed on thefirst housing shell 1342. Seals 1352 can be employed to seal theinterface between the housing 1340 and the first output member 16 andbetween the housing 1340 and the portion of the second planet carrier 76d that is rotatably coupled to the differential carrier 83.Additionally, a seal 1354 can be received in the housing 1356 in whichthe differential carrier 83 is disposed to seal the interface betweenthe housing 1356 and the portion of the second planet carrier 76 d thatis rotatably coupled to the differential carrier 83.

In FIGS. 11 and 12 of the drawings, portion of another axle assembly 10e constructed in accordance with the teachings of the present disclosureis illustrated. The axle assembly 10 e can include a torque distributiondrive mechanism 14 e that can be somewhat similar to the drive mechanism14 d of FIG. 7, except that the drive member 32 e and a clutch mechanism2000 cooperate to alternately provide rotary power that is employed bythe differential assembly 36 e for propulsive power or for the dualplanetary gear set 30 for torque vectoring control of the first andsecond output members 16 e and 18 e.

The drive mechanism 32 e can comprise any type of motor, such as a DCelectric motor 2004, and can have an output shaft 2006 that can beselectively operated to provide rotary power to a reduction drive 2010.The reduction drive 2010 can include a first pinion gear 2012, which canbe mounted to the output shaft 2006 for rotation therewith, and a secondpinion gear 2014 that can be mounted to an intermediate shaft 2016 forrotation therewith. The intermediate shaft 2016 can be disposed along anintermediate axis 2020 that is generally parallel to an output shaftaxis 2022 about which the output shaft 2006 of the motor 2004 rotates.The intermediate axis 2020 and the output shaft axis 2022 can beparallel to an axis 2024 about which the differential assembly 36 e andthe first and second output members 16 e and 18 e rotate. In theparticular example provided, the intermediate axis 2020, the outputshaft axis 2022 and the axis 2024 are disposed in a common plane, but itwill be appreciated that one or both of the intermediate axis 2024 andthe output shaft axis 2022 can be positioned differently. Moreover, itwill be appreciated that one or more spaced apart from the axis 2024 sothat one of the axes 2020, 2022 and 2024 will not lie in a common plane.While the reduction drive 2010 has been described and illustrated ashaving but a single pair of gears, it will be appreciated that thereduction drive could alternatively comprise additional gears disposedin a gear train between the first pinion gear 2012 and the second piniongear 2014.

With specific reference to FIG. 12, the intermediate shaft 2016 can havea first journal portion 2030, a second journal portion 2032 and a driveportion 2034 that can be disposed between the first and second journalportions 2030 and 2032. The drive portion 2034 can have a plurality ofexternal splines or teeth that can be meshingly engaged to a pluralityof internal splines or teeth that can be formed on a drive member 2038.A first intermediate output gear 2040 can be rotatably received on thefirst journal portion 2030 and a second intermediate output gear 2042can be rotatably received on the second journal portion 2032. Bearings2050 and 2052 can be received between the first and second journalportions 2030 and 2032 and the first and second intermediate outputgears 2040 and 2042, respectively. Thrust bearings 2054 can be disposedalong the length of the intermediate shaft 2016 at various locations tohelp promote relative rotation between the drive member 2038 and thefirst and second intermediate output gears 2040 and 2042.

The first intermediate output gear 2040 can be meshingly engaged to thering gear 1308 e of the differential assembly 36 e. As the ring gear1308 e is fixedly coupled to the differential carrier 83 e for commonrotation, it will be appreciated that rotation of the first intermediateoutput gear 2040 can cause corresponding rotation of the ring gear 1308e and the differential carrier 83 e, and that rotation of thedifferential carrier 83 e can similarly cause corresponding rotation ofthe first intermediate output gear 2040. The second intermediate outputgear 2042 can be meshingly engaged to an input gear 1314 e that isformed on the first ring gear 54 e. Accordingly, rotation of the secondintermediate output gear 2042 can cause corresponding rotation of theinput gear 1314 e and the first ring gear 54 e.

The clutch mechanism 2000 can be employed to control operation of thetorque distribution drive mechanism 14 e in a neutral condition (shown),a propulsion mode or a torque-vectoring mode. The clutch mechanism 2000can include a clutch collar 2060 having a set of internal teeth that canbe meshingly engaged to a set of external teeth formed on the drivemember 2038. Accordingly, rotation of the intermediate shaft 2016 willcause corresponding rotation of the clutch collar 2060. A first set ofclutch teeth 2070 can be formed on the first intermediate output gear2040 and a second set of clutch teeth 2072 can be formed on the secondintermediate output gear 2042. The clutch collar 2060 can be shiftedaxially along the intermediate axis 2020 such that the set of internalteeth formed on the clutch collar 2060 are engaged with the first set ofclutch teeth 2070 (to thereby couple the first intermediate output gear2040 to the intermediate shaft 2016 for common rotation), or such thatthe set of internal teeth formed on the clutch collar 2060 are engagedwith the second set of clutch teeth 2072 (to thereby couple the secondintermediate output gear 2042 to the intermediate shaft 2016 for commonrotation), or such that the set of internal teeth formed on the clutchcollar 2060 are not engaged to either the first set of clutch teeth 2070or the second set of clutch teeth 2072 (so that neither of the first andsecond intermediate output gears 2040 and 2042 is coupled to theintermediate shaft 2016 for rotation therewith).

Any type of actuator can be employed to axially move the clutch collar2060 along the intermediate axis 2020. In the particular exampleprovided, a clutch fork 2090 is employed to control the axial positionof the clutch collar 2060.

Operation of the clutch mechanism 2000 in a first mode (i.e., propulsionmode) can couple the first intermediate output gear 2040 to theintermediate shaft 2016 (via the clutch collar 2060) to thereby drivethe ring gear 1308 e of the differential assembly 36 e. As will beappreciated, rotation of the ring gear 1308 drives the differentialcarrier 83 e and the cross-pin 110 for rotation about the output axis2024. Pinion gears 112 are rotatably disposed on the cross-pin 110 andmeshingly engaged with first and second side gears 100 and 102. Thefirst side gear 100 is drivingly engaged to the first output member 16 eand the second side gear 102 is drivingly engaged to the second outputmember 18 e. In this mode, the dual planetary gearset 30 does not effectoperation of the differential assembly 36 e and as such, thedifferential assembly 36 e provides rotary power to the first and secondoutput members 16 e and 18 e in the manner of a standard opendifferential assembly.

Operation of the clutch mechanism 2000 in a second mode (i.e., torquevectoring mode) can couple the second intermediate output gear 2042 tothe intermediate shaft 2016 (via the clutch collar 2060) to therebydrive the input gear 1314 e and the first ring gear 54 e of the dualplanetary transmission 30. In this embodiment, rotary power is outputfrom the first planetary gearset 40 e to the differential carrier 83 e(via the first planet carrier 56 e) and rotary power is output from thesecond planetary gearset 42 e to the second output member 18 e (via thesecond planet carrier 76 e). As the second output member 18 e isnon-rotatably coupled the second side gear 102, it will be appreciatedthat the second planet carrier 76 e is also drivingly coupled to thesecond side gear 102. Those of skill in the art will appreciate fromthis disclosure that the dual planetary transmission 30 can be employedto impose an equal but opposite torque difference on the first andsecond output members 16 e and 18 e and that the amount of torqueapplied to a given one of the output members is dependent upon thedirection in which the motor 2004 is operated.

It will be appreciated that the above description is merely exemplary innature and is not intended to limit the present disclosure, itsapplication or uses. While specific examples have been described in thespecification and illustrated in the drawings, it will be understood bythose of ordinary skill in the art that various changes may be made andequivalents may be substituted for elements thereof without departingfrom the scope of the present disclosure as defined in the claims.Furthermore, the mixing and matching of features, elements and/orfunctions between various examples is expressly contemplated herein,even if not specifically shown or described, so that one of ordinaryskill in the art would appreciate from this disclosure that features,elements and/or functions of one example may be incorporated intoanother example as appropriate, unless described otherwise, above.Moreover, many modifications may be made to adapt a particular situationor material to the teachings of the present disclosure without departingfrom the essential scope thereof. Therefore, it is intended that thepresent disclosure not be limited to the particular examples illustratedby the drawings and described in the specification as the best modepresently contemplated for carrying out the teachings of the presentdisclosure, but that the scope of the present disclosure will includeany embodiments falling within the foregoing description and theappended claims.

What is claimed is:
 1. An axle assembly comprising: first and secondaxle shafts; a differential assembly having a differential carrier andfirst and second differential outputs received in the differentialcarrier that are rotatable about an output axis, the first differentialoutput being drivingly coupled to the first axle shaft, the seconddifferential output being drivingly coupled to the second axle shaft; ahousing; and a transmission received in the housing, the transmissionhaving first and second planetary gearsets, the first planetary gearsethaving a first ring gear, a first planet carrier and a first sun gear,the first planet carrier being coupled to one of the differentialcarrier and the second axle shaft for common rotation, the secondplanetary gearset having a second ring gear, a second planet carrier anda second sun gear, the second planet carrier being coupled to the otherone of the differential carrier and the second axle shaft for commonrotation, the second sun gear being coupled to the first sun gear forcommon rotation, wherein one of the first and second ring gears isfixedly coupled to the housing.
 2. The axle assembly of claim 1, furthercomprising a motor and reduction gearset coupled to the housing, themotor and reduction gearset being selectively operable for driving thesecond ring gear.
 3. The axle assembly of claim 2, further comprising: abevel ring gear coupled to the differential carrier for common rotation;and an input pinion meshingly engaged to the bevel ring gear.
 4. Theaxle assembly of claim 3, wherein the motor and reduction gearsetcomprises a worm and a worm gear.
 5. The axle assembly of claim 4,wherein the worm is formed on the outer periphery of the second ringgear.
 6. The axle assembly of claim 2, wherein the motor and reductiongearset comprises first and second gears that are meshingly engaged toone another and wherein the first and second gears are disposed forrotation about respective rotational axes that are parallel to oneanother, and wherein the rotational axis of the first gear is parallelto the output axis.
 7. The axle assembly of claim 6, wherein therotational axes of the first and second gears and the output axis aredisposed in a common plane.
 8. The axle assembly of claim 2, furthercomprising a clutch that is selectively operable in a first mode fortransmitting rotary power between the motor and reduction gearset andthe differential carrier.
 9. The axle assembly of claim 8, wherein theclutch comprises a collar that is axially slidable along the outputaxis.
 10. The axle assembly of claim 8, wherein the clutch isselectively operable in a second mode for driving the other one of thefirst and second ring gears.
 11. An axle assembly comprising: first andsecond axle shafts; a differential assembly having a differentialcarrier and first and second differential outputs received in thedifferential carrier that are rotatable about an output axis, the firstdifferential output being drivingly coupled to the first axle shaft, thesecond differential output being drivingly coupled to the second axleshaft; a housing; and a transmission received in the housing, thetransmission having a pair of planetary gearsets, each of the planetarygearsets having a ring gear, a planet carrier and a sun gear, whereinone of the ring gears is non-rotatably coupled to the housing, whereinone of the planet carriers is coupled for rotation with one of the firstand second differential outputs and the other one of the planet carriersis coupled to the differential case for rotation therewith, and whereinthe sun gears are non-rotatably coupled to one another.
 12. The axleassembly of claim 11, further comprising a motor and reduction gearsetcoupled to the housing, the motor and reduction gearset beingselectively operable for driving the ring gear that is not non-rotatablycoupled to the housing.
 13. The axle assembly of claim 12, wherein themotor and reduction gearset comprises a worm and a worm gear.
 14. Theaxle assembly of claim 13, wherein the worm is formed on the outerperiphery of the ring gear that is not non-rotatably coupled to thehousing.
 15. The axle assembly of claim 12, wherein the motor andreduction gearset comprises first and second gears that are meshinglyengaged to one another and wherein the first and second gears aredisposed for rotation about respective rotational axes that are parallelto one another, and wherein the rotational axis of the first gear isparallel to the output axis.
 16. The axle assembly of claim 15, whereinthe rotational axes of the first and second gears and the output axisare disposed in a common plane.
 17. The axle assembly of claim 11,further comprising a clutch that is selectively operable in a first modefor transmitting rotary power between the motor and reduction gearsetand the ring gear that is not non-rotatably coupled to the housing. 18.The axle assembly of claim 17, wherein the clutch comprises a collarthat is axially slidable along the output axis.
 19. The axle assembly ofclaim 17, wherein the clutch is selectively operable in a second modefor driving the differential carrier.
 20. The axle assembly of claim 19,wherein the clutch locks the transmission when the clutch is operated inthe second mode.
 21. The axle assembly of claim 11, further comprising:a bevel ring gear coupled to the differential carrier for commonrotation; and an input pinion meshingly engaged to the bevel ring gear.